/**

  * 加深对事件处理机制的理解

  * 通过光标的上下左右键,控制小球的左右上下移动.

  */

 package com.test4;

 import java.awt.*;

 import java.awt.event.*;

 import javax.swing.*;

 public class Demo9_4 extends JFrame {

     MyPanel mp = null;

     public static void main(String[] args) {

             Demo9_4 demo9_4 = new Demo9_4();

     }

     public Demo9_4(){

         mp = new MyPanel();

         this.add(mp);

         this.addKeyListener(mp);

         this.setSize(400,300);

         this.setVisible(true);

     }

 }

 //事件源JFrame->Demo9_4,MyPanel监听者,需要画小球

 //定义自己的面板

 class MyPanel extends JPanel implements KeyListener{

     int x=10;

     int y=10;

     public void paint(Graphics g){

         super.paint(g);

         g.fillOval(x, y, 10, 10);

     }

     @Override

     public void keyTyped(KeyEvent e) {//输入可以以显示的

     }

     @Override

     public void keyPressed(KeyEvent e) {//按下去.

 //        System.out.println(e.getKeyCode()==37);

         if(e.getKeyCode()==KeyEvent.VK_DOWN){

             y+=10;

         }else if(e.getKeyCode()==KeyEvent.VK_UP){

             y--;

         }else if(e.getKeyCode()==KeyEvent.VK_LEFT){

             x--;

         }else if(e.getKeyCode()==KeyEvent.VK_RIGHT){

             x++;

         }

         this.repaint();

     }

     @Override

     public void keyReleased(KeyEvent e) {//松开

     }

 }